1. Field of the Invention
This invention relates to the field of electrical interconnection devices, and more specifically to the field of bus connectors for portable computers.
2. Background Information
As technology grows the demand for faster more compact computers has increased. In order to reduce the size of computers and make them more portable, semiconductor devices have become and continue to become much smaller. Additionally, the layout of the semiconductor devices within a computer have become more dense. Smaller devices and more dense layouts have lead to more delicate devices and expensive repair costs.
Memory modules, for example, have become much smaller and as such the memory bus connectors within the computer itself have become smaller and more delicate. However, as technology advances computer users want to be able to easily upgrade the memory modules in their existing computer systems. Thus, it is important in the design of memory modules and memory bus connectors that they are able to withstand some abuse by the computer user when upgrading the memory modules while still maintaining the smaller and more dense layouts.
In portable computers, the space limitations have also made it important to design memory modules and memory bus connectors in a manner that would hold the memory module in a plane parallel to the motherboard rather than perpendicular to it. As illustrated in FIG. 1, memory bus connector 120 holds the memory module 100 in a horizontal fashion such that the memory module 100 is parallel to motherboard 130. The parallel memory module 100 allows the portable computer to be manufactured in thinner and smaller cases improving the portability of the computer.
Vertical memory boards which are used in desktop computers take up much more room and would require more space than is available in a portable computer such as a laptop computer. As illustrated in FIG. 2, memory bus connector 220 holds memory module 200 in a vertical fashion such that the memory module 200 is perpendicular to motherboard 230. A vertical memory module 200 would increase the thickness and overall size of the portable computer making the portable computer too big and bulky.
With parallel memory modules, however, come additional concerns. For example, a Small Outline Dual In Line Memory Module (SO-DIMM) contains about 144 individual contacts. Thus, the memory bus connector that connects the SO-DIMM to the motherboard has a corresponding number of contacts (or leads). As illustrated in FIG. 3, a prior art memory bus connector 120, which would hold the memory module 100 parallel to the motherboard, contains top leads 141 and bottom leads 142 which interconnect to the memory module 100. In the case of the SO-DIMM, memory bus connector 120 would have seventy-two (72) individual top leads 141 and seventy-two (72) individual bottom leads 142, as illustrated in FIG. 4. FIG. 5 illustrates an enlargement of a portion of the memory bus connector 120 illustrated in FIG. 4.
The individual top leads 141 and individual bottom leads 142 may be any combination of data signal contacts and ground members depending upon the contact layout of the particular memory module being used. Thus, there could be data signal contacts in both the top and bottom leads and there could also be ground members in both the top and bottom leads. Because the memory module 100 is parallel to the motherboard (i.e. horizontal), the top and bottom leads 141 & 142 are different lengths. The top leads 141 must be longer and bend up and over in order to connect the upper portion of the memory module to the motherboard and the bottom leads 142 are shorter since they connect the lower portion of the memory module to the motherboard.
One problem with this prior art design is that because the top leads 141 are longer, they necessarily have higher inductances. These higher inductances are not an issue for memory buses at present speeds (typically 66-100 MHz), but will become impediments to proper operation of future memory buses, where speeds of 400 MHz to 1 GHz are anticipated.
Another problem with the prior art design for the memory bus connector, illustrated in FIG. 4, is that there are no means for providing controlled characteristic impedances to the signal contacts. The ability to control characteristic impedances is common in other high-speed interconnection schemes, for example, backplanes. In a direct Rambus DRAM memory module it is desirable to have the ability to control the characteristic impedance to approximately 28 ohms.
In the vertical memory module 200 (illustrated in FIG. 2) the connecting leads in the memory bus connector 220 are all the same length and are very short (simply the distance from the motherboard to the connection on the memory module). The leads for the vertical memory module do not have to reach up and around the vertical memory module as they do in the horizontal (or parallel) memory module. Thus the vertical memory module and memory bus connector used in desktop computers do not have a significant problem with inductance.
What is needed is a memory bus connector that solves the problem of inductance that is prevalent in the parallel memory module design of portable computers. Additionally, what is needed is a memory bus connector that solves the problem of characteristic impedance that is also prevalent in the parallel memory module design of portable computers.